Tudor domain containing (Tdrd) proteins that are expressed in germ cells are divided into two groups. One group, consisting of TDRD1, TDRKH, TDRD9 and TDRD12, function in piRNA biogenesis and retrotransposon silencing, while the other group including RNF17/TDRD4 and TDRD5-7 are required for spermiogenesis. These Tdrd proteins play distinct roles during male germ cell development. Here, we report the characterization of STK31/TDRD8 in mice. STK31 contains a tudor domain and a serine/threonine kinase domain. We find that STK31 is a cytoplasmic protein in germ cells. STK31 is expressed in embryonic gonocytes of both sexes and postnatal spermatocytes and round spermatids in males. Disruption of the tudor domain and kinase domain of STK31 respectively does not affect fertility in mice. Our data suggest that the function of STK31 may be redundant with other Tdrd proteins in germ cell development.